The present invention relates generally to signal coupling devices. More particularly, the present invention is directed to a signal coupler which transmits information in the form of heat pulses which are received by a pyroelectric detector.
There are numerous well-known techniques in the electronic packaging and interconnection art to form high-speed (e.g, 1 MHz to 1 GHz) data communication links between two electronic circuit boards, substrates, packaging layers, circuit elements or the like. This problem may be described in respect to the particular packaging problem of coupling electronic data signals between two circuit boards, although it will be understood that many of the same considerations apply to the signal coupling problems associated with other types of electronic packaging.
The most common way to form high-speed data links between two circuit boards is to form data transmission lines and signal contact pads on each circuit board. Low resistance bonds between the signal contact pads of the two boards are formed using solder bonds or conductive epoxy bonds. One drawback of conventional bonding processes used to interconnect two circuit boards is that the parasitic electrical resistance increases rapidly as the area of the contact pads decreases. Typically, signal contact pads must have a diameter of greater than about 100 microns in order to maintain a low contact resistance. Another drawback is that solder and epoxy bond connections are relatively permanent, i.e., it is typically not possible to cheaply, reliably, and quickly remove the two boards after the permanent conductive joints have been formed.
The electronics art also includes detachable mechanical signal connectors for forming a removable electrical connection between two different circuit boards or substrates. Commonly, these connectors comprise female electrical sockets on a first board designed to mate with complementary male elements disposed on a second board. Conventional male/female connectors have many drawbacks. One drawback is that the sockets increase the electrical resistance and add a parasitic inductance. The parasitic electrical resistance and inductance of the connector may limit the rate at which data can be communicated. Another drawback is that male/female connectors tend to have a substantial size compared to the circuit boards themselves. Still another drawback is that it is difficult to form a reliable male/female connection as the contact area of the male/female elements is reduced. A direct pressure contact between two electrical contact surfaces often results in only a fraction of the metallic surfaces forming an electrical conductive pathway for the flow of current, resulting in a high contact resistance. This problem is particularly severe as the male/female connector is miniaturized. Consequently, it is difficult to form a high density of electrical interconnections using male/female sockets.
Conventional means for interconnecting two circuit boards do not permit a compact, high speed, removable signal coupler to be achieved. This limits the ability of circuit designers and packaging engineers to test, assemble, or disassemble signal data links between circuit boards, substrates, and multi-chip modules.
What is desired is a compact, removable, low stress signal coupler for forming a data communication link between two circuit boards, substrates, or the like.
The present invention is a signal coupler for transmitting data signals between two substrates, circuit boards, or the like, which utilizes the pyroelectric effect. A transmitting section of the signal coupler generates thermal pulses in the pyroelectric detector element of a receiving section, thereby communicating data signals.
The receiving section of the present invention generally includes: a support layer; a pyroelectric film disposed on a surface of the support layer, the pyroelectric film having first and second opposed film surfaces; a thermally conductive member disposed in the support layer coupled to said pyroelectric film; first and second electrical contacts coupled to the pyroelectric film configured to couple an electrical output signal from the pyroelectric film; wherein the pyroelectric film is composed of a pyroelectric polymer having a greater than about 1% by volume of a high thermal dipuffusivity electrically insulating material so that the pyroelectric film has a thermal diffusivity at least ten times greater than the thermal diffusivity of the bulk polymer. In a preferred embodiment, the support layer is disposed on a thermally conductive substrate and the pyroelectric film is a pyroelectric film element which has a thickness less than about 200 nanometers.
The transmitting section of the present invention includes a substrate having an energy source configured to generate thermal pulses which are received by the pyroelectric film element of the receiving section. In a preferred embodiment, the energy source is a thin film resistive heating element disposed on a thermally insulating portion of a substrate. Heat pulses generated by the resistive heating element are thermally conducted to the pyroelectric film element of the receiving section by a thermally conductive film, preferably a thin film of thermal grease. In an alternate embodiment, the thermal energy source is a semiconductor laser which generates infrared laser pulses which are received as heat puls pyroelectric film element.
One object of the present invention is to provide a low contact pressure signal coupler which is removable and which does not require permanent mechanical bonds to be made between the transmitting and receiving sections of the signal coupler.
Another object of the present invention is a receiving section with a pyroelectric film element which is capable of receiving data at rates in excess of one million bits per second.
Still another object of the- present invention is transmitting section which efficiently generates thermal pulses in the receiving section.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description and from the detailed drawings.